1. Field of Invention
The invention relates to a method of manufacturing a thin film transistor and a substrate structure thereof.
2. Related Art
In recent years, the use of computers and the internet has provided another access to information. People have become more familiar with gaining their information from computers rather than books. However, the way people used to read is not easy to change; therefore paper still plays an important role as an information carrier. With the development of display technology, a display can be lighter, thinner, and more portable and flexible. For example, the development of electronic paper has attracted many investors' attention. As a result, many companies have been rushing to develop this kind of technique so as not to miss another “paper revolution.”
The organic thin film transistor (OTFT) is designed by choosing an appropriate organic material that is suitable for being the transistor material of an electronic device. For example, when a panel consisting of the OTFT is bended, the property of the OTFT can remain the same and the image displayed will not be affected. Therefore, the OTFT technique accelerates the achievement of flexible electronic products, such as a flexible display. Also, because a plastic substrate is transparent, light, thin, impact resistant, flexible and suitable for the roll to roll ink injecting high efficiency process, an increasing tendency is to use a plastic substrate to form an OTFT thereon when manufacturing a flexible display or logical device. However, there is not only the problem of how to improve the oxygen and water permeability of the substrate in the plastic substrate process, but also the problem of inaccurate alignment caused by the varied size of the substrate during solvent rinsing and high temperature process. Thus, this process is difficult and causes a low yield.
FIG. 1 is a conventional organic thin film transistor which uses a plastic substrate as a base. In order to improve production efficiency, a large size plastic substrate will form many thin film transistors thereon at once. For process control and management purposes, the large size plastic substrate will be divided into several blocks, such as P02, P03, P04, P05, P06 . . . , and each block will further be divided into several units. For example, the P06 block can further be divided into A0, A1 . . . , A8, G0, G1 . . . , and G8 units. Besides, an alignment area 92 will be provided in each process as a reference for alignment.
FIG. 2 is a diagram showing a conventional plastic substrate with variation in size after the thermal process in the thin film transistor manufacturing process. Take the P06 block as an example; the A0, A8, G0, G8 units are located at four corners of the P06 block respectively. By adding the imagined vertical and horizontal supplementary lines, it is found that the four units have different extents after the thermal process, therefore producing a vertical offset of D1 and a horizontal offset of D2. These offsets may seriously affect the accuracy of the alignment and may further make the thin film transistors unstable or inconsistent if the inaccuracy problem is not solved. Besides, because different types of plastic substrate have different extents of thermal expansion, it complicates the process and increases the cost if a different plastic substrate is applied every time and a different mask has to be provided.